The ordinary CD lens cleaners are pretty good for instant-but-temporary fixes...enough to help you make it through the night....(Wasnt that a song?

)
My theory is that the CD lens cleaners with the line of miniture brushes on them help create a little whirlwind inside the CD assembly, simply blowing any loose bits of fluff (

) off of the laser lens. Temporary, but for the sake of £5~10, its better to have one with you at a gig, than not.
Be aware, however, that some CD-decks state that you must NOT use certain CD cleaner discs. - check your manuals for details.
....then get the lens drunk with the above fluid, when you've got a few hours and a screw driver around.